9V Battery ground and Power supply ground

Discussion in 'General Electronics Discussion' started by electronicsLearner77, Oct 4, 2020.

1. electronicsLearner77

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Jul 2, 2015
I want to know the difference between the 9V battery negative (can it be called the ground?) and the power supply ground? The 9V battery has negative terminal is it same as the source ground which is connected to the mains.

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Nov 8, 2019
3. Harald KappModeratorModerator

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Nov 17, 2011
Just to make sure: do not connect y battery to mains - unless you really know what you are doing. Don't!

The concept of "ground" has many facets, here are just two of them:
• The "ground" you refer to in connection with mains is usually a protective ground connected to earth, i.e. the same potential you have. It is therefore often called "earth", too. You can see the connection between "ground" and "earth", I think. Two names one thing: The ground/earth you are standing on. This is used for safety purposes as a short circuit from mains' life to ground will trigger the circuit breaker, interrupting current flow ideally before any harm is done to a human.
• "Ground" is for historical reasons also used to label the reference potential within an electric/electronic circuit. It is named so because historically this reference potential really was connected to ground/earth. But this doesn'T have to be so, as you can easily see when looking at a battery operated device without any direct connection to ground/earth.
So why a reference potential? A voltage can only exist as a potential difference between two point. You cannot measure the voltage of a single point (connect e.g. the "+" input of a voltmeter to the "+" pole of a batters without connecting "-" also: the meter will show 0 V). When measuring voltage in a circuit you therefore need a reference potential. With a single power supply (battery), it is common to use the "-" pole as the reference potential. Thus the supply voltage will be positive and so will be any voltage you measure in your circuit (with reference to "ground").
The discussion in the link from @bertus goes a bit further discussing dual supplies (having both a positive an a negative supply). Read through the discussion, I think you will find your thoughts being picked up there.

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